diff --git a/c4.c b/c4.c
index a6d07bd..2f383ea 100644
--- a/c4.c
+++ b/c4.c
@@ -1,600 +1,600 @@
-// c4.c - C in four functions
-
-// char, int, and pointer types
-// if, while, return, and expression statements
-// just enough features to allow self-compilation and a bit more
-
-// Written by Robert Swierczek
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <memory.h>
-#include <unistd.h>
-
-char *p, *lp, // current position in source code
-     *data;   // data/bss pointer
-
-int *e, *le,  // current position in emitted code
-    *id,      // currently parsed identifier
-    *sym,     // symbol table (simple list of identifiers)
-    tk,       // current token
-    ival,     // current token value
-    ty,       // current expression type
-    loc,      // local variable offset
-    line,     // current line number
-    src,      // print source and assembly flag
-    debug;    // print executed instructions
-
-// tokens and classes (operators last and in precedence order)
-/*
-
-Id = identifier 用户定义的identifier
-
-//运算符
-Assign  =
-Cond    ?
-Lor     ||
-Lan     &&
-Or      |
-Xor     ^
-And     &
-Eq      ==
-Ne      !=
-Lt      <
-Gt      >
-Le      <=
-Ge      >=
-Shl     <<
-Shr     >>
-Add     +
-Sub     -
-Mul     *
-Div     /
-Mod     %
-Inc     ++
-Dec     --
-Brak    [
-*/
-/*
-id[Class] =
-Num  常量数值
-Fun 函数
-Sys 系统调用
-Glo 全局变量
-Loc 局部变量
-*/
-enum {
-  Num = 128, Fun, Sys, Glo, Loc, Id,
-  Char, Else, Enum, If, Int, Return, Sizeof, While,
-  Assign, Cond, Lor, Lan, Or, Xor, And, Eq, Ne, Lt, Gt, Le, Ge, Shl, Shr, Add, Sub, Mul, Div, Mod, Inc, Dec, Brak
-};
-
-// opcodes
-enum { LEA ,IMM ,JMP ,JSR ,BZ  ,BNZ ,ENT ,ADJ ,LEV ,LI  ,LC  ,SI  ,SC  ,PSH ,
-       OR  ,XOR ,AND ,EQ  ,NE  ,LT  ,GT  ,LE  ,GE  ,SHL ,SHR ,ADD ,SUB ,MUL ,DIV ,MOD ,
-       OPEN,READ,CLOS,PRTF,MALC,MSET,MCMP,EXIT };
-
-// types
-enum { CHAR, INT, PTR };
-
-// identifier offsets (since we can't create an ident struct)
-//因为作者没有实现结构体,所以[id]指向的空间被分割为Idsz大小的块(模拟结构体)
-//当id指向块首时,id[0] == id[Tk] 访问的就是Tk成员的数据(一般是指针)
-//Name 指向的是这个identifier的Name
-//Type 为数据类型(比如返回值类型),如CHAR,INT,INT+PTR
-//Class 为类型,如Num(常量数值),Fun(函数),Sys(系统调用),Glo全局变量,Loc 局部变量
-enum { Tk, Hash, Name, Class, Type, Val, HClass, HType, HVal, Idsz };
-
-//词法分析
-void next()
-{
-  char *pp;
-  // 用循环来忽略空白字符,不过不能被词法分析器识别的字符都被认为是空白字符 比如 '@', '$'
-  while (tk = *p) {
-    ++p;
-    if (tk == '\n') {
-      if (src) { //命令行指明-s参数,输出源代码和对应字节码
-        printf("%d: %.*s", line, p - lp, lp);
-        lp = p;
-        while (le < e) {
-          printf("%8.4s", &"LEA ,IMM ,JMP ,JSR ,BZ  ,BNZ ,ENT ,ADJ ,LEV ,LI  ,LC  ,SI  ,SC  ,PSH ,"
-                           "OR  ,XOR ,AND ,EQ  ,NE  ,LT  ,GT  ,LE  ,GE  ,SHL ,SHR ,ADD ,SUB ,MUL ,DIV ,MOD ,"
-                           "OPEN,READ,CLOS,PRTF,MALC,MSET,MCMP,EXIT,"[*++le * 5]);
-          if (*le <= ADJ) printf(" %d\n", *++le); else printf("\n"); //ADJ之前的指令均有操作数
-        }
-      }
-      ++line;
-    }
-    else if (tk == '#') {//#作为单行注释符号,处理#include等情况
-      while (*p != 0 && *p != '\n') ++p;
-    }
-    else if ((tk >= 'a' && tk <= 'z') || (tk >= 'A' && tk <= 'Z') || tk == '_') {
-      pp = p - 1; //因为有++p,pp回退一个字符,pp指向 [这个符号] 的首字母
-      while ((*p >= 'a' && *p <= 'z') || (*p >= 'A' && *p <= 'Z') || (*p >= '0' && *p <= '9') || *p == '_')
-        tk = tk * 147 + *p++;//计算哈希值,tk起始时已经等于*p,从p开始正确
-      tk = (tk << 6) + (p - pp); //哈希值加上[符号长度]
-      id = sym;
-      while (id[Tk]) {
-        if (tk == id[Hash] && !memcmp((char *)id[Name], pp, p - pp)) {
-          //找到同名,则tk = id[Tk] (将id看做结构体,访问其Tk成员,解释见上)
-          tk = id[Tk];
-          return;
-        }
-        id = id + Idsz;//继续循环identifier表
-      }
-      //找不到,发现新identifier,此时id已经指向新的identifier结构
-      id[Name] = (int)pp;
-      id[Hash] = tk;//哈希值
-      tk = id[Tk] = Id; //token 类型为identifier
-      return;
-    }
-    else if (tk >= '0' && tk <= '9') {// 第一位为数字,认为是数值
-      if (ival = tk - '0') { while (*p >= '0' && *p <= '9') ival = ival * 10 + *p++ - '0'; }//第一位不为0,认为是十进制数
-      else if (*p == 'x' || *p == 'X') {//第一位为0,且以x开头,认为是16进制数
-        while ((tk = *++p) && ((tk >= '0' && tk <= '9') || (tk >= 'a' && tk <= 'f') || (tk >= 'A' && tk <= 'F')))
-          ival = ival * 16 + (tk & 15) + (tk >= 'A' ? 9 : 0);
-      }
-      else { while (*p >= '0' && *p <= '7') ival = ival * 8 + *p++ - '0'; }//认为是八进制数
-      tk = Num;//token 为数值型,返回
-      return;
-    }
-    else if (tk == '/') {
-      if (*p == '/') {//两个'/'开头,单行注释
-        ++p;
-        while (*p != 0 && *p != '\n') ++p;
-      }
-      else {
-        tk = Div; //除法
-        return;
-      }
-    }
-    else if (tk == '\'' || tk == '"') {//引号开头,认为是字符(串)
-      pp = data;
-      while (*p != 0 && *p != tk) {//直到找到匹配的引号为止;p == 0 是什么情况没看懂;
-        if ((ival = *p++) == '\\') {
-          if ((ival = *p++) == 'n') ival = '\n';// '\n' 认为是'\n' 其他直接忽略'\'转义
-        }
-        if (tk == '"') *data++ = ival;//如果是双引号,认为是字符串,向data拷贝字符
-      }
-      ++p;
-      if (tk == '"') ival = (int)pp; else tk = Num;//双引号则ival指向data中字符串开始,单引号则认为是数字
-      return;
-    }
-    else if (tk == '=') { if (*p == '=') { ++p; tk = Eq; } else tk = Assign; return; }//等于,赋值
-    else if (tk == '+') { if (*p == '+') { ++p; tk = Inc; } else tk = Add; return; }//加,自增
-    else if (tk == '-') { if (*p == '-') { ++p; tk = Dec; } else tk = Sub; return; }//减,自减
-    else if (tk == '!') { if (*p == '=') { ++p; tk = Ne; } return; }//不等于
-    else if (tk == '<') { if (*p == '=') { ++p; tk = Le; } else if (*p == '<') { ++p; tk = Shl; } else tk = Lt; return; }// <,<=, <<
-    else if (tk == '>') { if (*p == '=') { ++p; tk = Ge; } else if (*p == '>') { ++p; tk = Shr; } else tk = Gt; return; }//>,>= >>
-    else if (tk == '|') { if (*p == '|') { ++p; tk = Lor; } else tk = Or; return; }//逻辑或,或
-    else if (tk == '&') { if (*p == '&') { ++p; tk = Lan; } else tk = And; return; }
-    else if (tk == '^') { tk = Xor; return; }
-    else if (tk == '%') { tk = Mod; return; }
-    else if (tk == '*') { tk = Mul; return; }
-    else if (tk == '[') { tk = Brak; return; }
-    else if (tk == '?') { tk = Cond; return; }
-    else if (tk == '~' || tk == ';' || tk == '{' || tk == '}' || tk == '(' || tk == ')' || tk == ']' || tk == ',' || tk == ':') return;//不做处理
-  }
-}
-//表达式分析
-//lev表示运算符,因为各个运算符token是按照优先级生序排列的,所以lev大表示优先级高
-void expr(int lev)
-{
-  int t, *d;
-
-  if (!tk) { printf("%d: unexpected eof in expression\n", line); exit(-1); }
-  else if (tk == Num) { *++e = IMM; *++e = ival; next(); ty = INT; } //直接取立即数作为表达式值
-  else if (tk == '"') { //字符串
-    *++e = IMM; *++e = ival; next();
-    while (tk == '"') next();//连续的'"' 处理C风格多行文本 比如["abc" "def"]
-    data = (char *)((int)data + sizeof(int) & -sizeof(int));//字节对齐到int
-    ty = PTR;
-  }
-  else if (tk == Sizeof) {
-    next(); if (tk == '(') next(); else { printf("%d: open paren expected in sizeof\n", line); exit(-1); }
-    ty = INT; if (tk == Int) next(); else if (tk == Char) { next(); ty = CHAR; }
-    while (tk == Mul) { next(); ty = ty + PTR; }//多级指针,每多一级加PTR
-    if (tk == ')') next(); else { printf("%d: close paren expected in sizeof\n", line); exit(-1); }
-    *++e = IMM; *++e = (ty == CHAR) ? sizeof(char) : sizeof(int);//除了char是一字节,int和多级指针都是int大小
-    ty = INT;
-  }
-  else if (tk == Id) {//identifier
-    d = id; next();
-    if (tk == '(') {//函数
-      next();
-      t = 0;//形参个数
-      while (tk != ')') { expr(Assign); *++e = PSH; ++t; if (tk == ',') next(); }//计算实参的值，压栈(传参)
-      next();
-      if (d[Class] == Sys) *++e = d[Val]; //系统调用,如malloc,memset,d[val]为opcode
-      else if (d[Class] == Fun) { *++e = JSR; *++e = d[Val]; } //用户定义函数,d[Val]为函数入口地址
-      else { printf("%d: bad function call\n", line); exit(-1); }
-      if (t) { *++e = ADJ; *++e = t; }//因为用栈传参,调整栈
-      ty = d[Type];//函数返回值类型
-    }
-    else if (d[Class] == Num) { *++e = IMM; *++e = d[Val]; ty = INT; }//d[Class] == Num,处理枚举(只有枚举是Class==Num)
-    else {//变量
-      //变量先取地址然后再LC/LI
-      if (d[Class] == Loc) { *++e = LEA; *++e = loc - d[Val]; }//取地址,d[Val]是局部变量偏移量
-      else if (d[Class] == Glo) { *++e = IMM; *++e = d[Val]; }//取地址,d[Val] 是全局变量指针
-      else { printf("%d: undefined variable\n", line); exit(-1); }
-      *++e = ((ty = d[Type]) == CHAR) ? LC : LI;
-    }
-  }
-  else if (tk == '(') {
-    next();
-    if (tk == Int || tk == Char) {//强制类型转换
-      t = (tk == Int) ? INT : CHAR; next();
-      while (tk == Mul) { next(); t = t + PTR; }//指针
-      if (tk == ')') next(); else { printf("%d: bad cast\n", line); exit(-1); }
-      expr(Inc); //高优先级
-      ty = t;
-    }
-    else { //一般语法括号
-      expr(Assign);
-      if (tk == ')') next(); else { printf("%d: close paren expected\n", line); exit(-1); }
-    }
-  }
-  else if (tk == Mul) {//取指针指向值
-    next(); expr(Inc);//高优先级
-    if (ty > INT) ty = ty - PTR; else { printf("%d: bad dereference\n", line); exit(-1); }
-    *++e = (ty == CHAR) ? LC : LI;
-  }
-  else if (tk == And) {//&,取地址操作
-    next(); expr(Inc);
-    if (*e == LC || *e == LI) --e;//根据上面的代码,token为变量时都是先取地址再LI/LC,所以--e就变成了取地址到a
-    else { printf("%d: bad address-of\n", line); exit(-1); }
-    ty = ty + PTR;
-  }
-  else if (tk == '!') { next(); expr(Inc); *++e = PSH; *++e = IMM; *++e = 0; *++e = EQ; ty = INT; }//!x相当于 x==0
-  else if (tk == '~') { next(); expr(Inc); *++e = PSH; *++e = IMM; *++e = -1; *++e = XOR; ty = INT; }//~x 相当于x ^ -1
-  else if (tk == Add) { next(); expr(Inc); ty = INT; }
-  else if (tk == Sub) {
-    next(); *++e = IMM;
-    if (tk == Num) { *++e = -ival; next(); } //数值,取负
-    else { *++e = -1; *++e = PSH; expr(Inc); *++e = MUL; }//乘-1
-    ty = INT;
-  }
-  else if (tk == Inc || tk == Dec) {//处理++x,--x//x--,x++在后面处理
-    t = tk; next(); expr(Inc);
-    //处理++x,--x
-    if (*e == LC) { *e = PSH; *++e = LC; }//地址压栈(下面SC/SI用到),再取数
-    else if (*e == LI) { *e = PSH; *++e = LI; }
-    else { printf("%d: bad lvalue in pre-increment\n", line); exit(-1); }
-    *++e = PSH;//将数值压栈
-    *++e = IMM; *++e = (ty > PTR) ? sizeof(int) : sizeof(char);//指针则加减一字,否则加减1
-    *++e = (t == Inc) ? ADD : SUB;//运算
-    *++e = (ty == CHAR) ? SC : SI;//存回变量
-  }
-  else { printf("%d: bad expression\n", line); exit(-1); }
-
-  //爬山法
-  //tk为ASCII码的都不会超过Num=128
-  while (tk >= lev) { // "precedence climbing" or "Top Down Operator Precedence" method
-    t = ty;//ty在递归过程中可能会改变,所以备份当前处理的表达式类型
-    if (tk == Assign) { //赋值
-      next();
-      if (*e == LC || *e == LI) *e = PSH; //左边被tk=Id中变量部分处理过了,将地址压栈
-      else { printf("%d: bad lvalue in assignment\n", line); exit(-1); }
-      expr(Assign); *++e = ((ty = t) == CHAR) ? SC : SI;//取得右值expr的值,作为a=expr的结果
-    }
-    else if (tk == Cond) {//x?a:b和if类似,除了不能没有else
-      next();
-      *++e = BZ; d = ++e;
-      expr(Assign);
-      if (tk == ':') next(); else { printf("%d: conditional missing colon\n", line); exit(-1); }
-      *d = (int)(e + 3); *++e = JMP; d = ++e;
-      expr(Cond);
-      *d = (int)(e + 1);
-    }
-    else if (tk == Lor) { next(); *++e = BNZ; d = ++e; expr(Lan); *d = (int)(e + 1); ty = INT; }//短路,逻辑Or运算符左边为true则表达式为true,不用计算运算符右侧的值
-    else if (tk == Lan) { next(); *++e = BZ;  d = ++e; expr(Or);  *d = (int)(e + 1); ty = INT; }//短路,逻辑And,同上
-    else if (tk == Or)  { next(); *++e = PSH; expr(Xor); *++e = OR;  ty = INT; }//将当前值Push,计算运算符右边值,再与当前值(在栈中)做运算;
-    else if (tk == Xor) { next(); *++e = PSH; expr(And); *++e = XOR; ty = INT; }//expr中lev指明递归函数中最结合性不得低于哪一个运算符
-    else if (tk == And) { next(); *++e = PSH; expr(Eq);  *++e = AND; ty = INT; }
-    else if (tk == Eq)  { next(); *++e = PSH; expr(Lt);  *++e = EQ;  ty = INT; }
-    else if (tk == Ne)  { next(); *++e = PSH; expr(Lt);  *++e = NE;  ty = INT; }
-    else if (tk == Lt)  { next(); *++e = PSH; expr(Shl); *++e = LT;  ty = INT; }
-    else if (tk == Gt)  { next(); *++e = PSH; expr(Shl); *++e = GT;  ty = INT; }
-    else if (tk == Le)  { next(); *++e = PSH; expr(Shl); *++e = LE;  ty = INT; }
-    else if (tk == Ge)  { next(); *++e = PSH; expr(Shl); *++e = GE;  ty = INT; }
-    else if (tk == Shl) { next(); *++e = PSH; expr(Add); *++e = SHL; ty = INT; }
-    else if (tk == Shr) { next(); *++e = PSH; expr(Add); *++e = SHR; ty = INT; }
-    else if (tk == Add) {
-      next(); *++e = PSH; expr(Mul);
-      if ((ty = t) > PTR) { *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = MUL;  }//处理指针
-      *++e = ADD;
-    }
-    else if (tk == Sub) {
-      next(); *++e = PSH; expr(Mul);
-      if (t > PTR && t == ty) { *++e = SUB; *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = DIV; ty = INT; }//指针相减
-      else if ((ty = t) > PTR) { *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = MUL; *++e = SUB; }//指针减数值
-      else *++e = SUB;
-    }
-    else if (tk == Mul) { next(); *++e = PSH; expr(Inc); *++e = MUL; ty = INT; }
-    else if (tk == Div) { next(); *++e = PSH; expr(Inc); *++e = DIV; ty = INT; }
-    else if (tk == Mod) { next(); *++e = PSH; expr(Inc); *++e = MOD; ty = INT; }
-    else if (tk == Inc || tk == Dec) {//处理x++,x--
-      if (*e == LC) { *e = PSH; *++e = LC; }
-      else if (*e == LI) { *e = PSH; *++e = LI; }
-      else { printf("%d: bad lvalue in post-increment\n", line); exit(-1); }
-      *++e = PSH; *++e = IMM; *++e = (ty > PTR) ? sizeof(int) : sizeof(char);
-      *++e = (tk == Inc) ? ADD : SUB;//先自增/自减
-      *++e = (ty == CHAR) ? SC : SI;//存到内存里
-      *++e = PSH; *++e = IMM; *++e = (ty > PTR) ? sizeof(int) : sizeof(char);
-      *++e = (tk == Inc) ? SUB : ADD;//再相反操作,保证后自增/自减不影响这次表达式的求值
-      //PS:我终于知道哪些a=1;b=a+++a++为啥等于3了
-      next();
-    }
-    else if (tk == Brak) {//数组下标
-      next(); *++e = PSH; expr(Assign);//保存数组指针, 计算下标
-      if (tk == ']') next(); else { printf("%d: close bracket expected\n", line); exit(-1); }
-      if (t > PTR) { *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = MUL;  } //t==PTR时是Char,Char = 0
-      else if (t < PTR) { printf("%d: pointer type expected\n", line); exit(-1); }
-      *++e = ADD;
-      *++e = ((ty = t - PTR) == CHAR) ? LC : LI;
-    }
-    else { printf("%d: compiler error tk=%d\n", line, tk); exit(-1); }
-  }
-}
-
-//分析函数中除了声明之外的部分,语法分析
-void stmt()
-{
-  int *a, *b;
-
-  if (tk == If) {
-    next();
-    if (tk == '(') next(); else { printf("%d: open paren expected\n", line); exit(-1); }
-    expr(Assign);
-    if (tk == ')') next(); else { printf("%d: close paren expected\n", line); exit(-1); }
-    *++e = BZ; //branch if zero
-    b = ++e;//branch address pointer
-    stmt(); // 继续分析
-    if (tk == Else) {
-      *b = (int)(e + 3); // e + 3 位置是else 起始位置
-      *++e = JMP; // if 语句 else 之前插入 JMP 跳过Else 部分
-      b = ++e; // JMP目标
-      next();
-      stmt();//分析else 部分
-    }
-    *b = (int)(e + 1);//if 语句结束,无论是if BZ 跳转目标还是 else 之前的JMP的跳转目标
-  }
-  else if (tk == While) {//循环
-    next();
-    a = e + 1; // While 循环体起始地址
-    if (tk == '(') next(); else { printf("%d: open paren expected\n", line); exit(-1); }
-    expr(Assign);
-    if (tk == ')') next(); else { printf("%d: close paren expected\n", line); exit(-1); }
-    *++e = BZ; b = ++e;//b = While 语句结束后地址
-    stmt();//处理While 语句体
-    *++e = JMP; *++e = (int)a;//无条件跳转到While语句开始(包括循环条件的代码),实现循环
-    *b = (int)(e + 1);//BZ跳转目标(循环结束)
-  }
-  else if (tk == Return) {
-    next();
-    if (tk != ';') expr(Assign);//计算返回值
-    *++e = LEV;
-    if (tk == ';') next(); else { printf("%d: semicolon expected\n", line); exit(-1); }//What's this?
-  }
-  else if (tk == '{') {//复合语句
-    next();
-    while (tk != '}') stmt();
-    next();
-  }
-  else if (tk == ';') {
-    next();
-  }
-  else {
-    expr(Assign);//一般的语句认为是赋值语句/表达式
-    if (tk == ';') next(); else { printf("%d: semicolon expected\n", line); exit(-1); }
-  }
-}
-
-int main(int argc, char **argv)
-{
-  //fd file descriptor 文件描述
-  //bt basetype
-  //poolsz 一系列池的大小
-  int fd, bt, ty, poolsz, *idmain;
-  int *pc, *sp, *bp, a, cycle; // vm registers 虚拟器的寄存器
-  int i, *t; // temps
-
-  --argc; ++argv;
-  if (argc > 0 && **argv == '-' && (*argv)[1] == 's') { src = 1; --argc; ++argv; }
-  if (argc > 0 && **argv == '-' && (*argv)[1] == 'd') { debug = 1; --argc; ++argv; }
-  if (argc < 1) { printf("usage: c4 [-s] [-d] file ...\n"); return -1; }
-
-  if ((fd = open(*argv, 0)) < 0) { printf("could not open(%s)\n", *argv); return -1; }//打开文件
-
-  poolsz = 256*1024; // arbitrary size
-  if (!(sym = malloc(poolsz))) { printf("could not malloc(%d) symbol area\n", poolsz); return -1; }//符号表
-  if (!(le = e = malloc(poolsz))) { printf("could not malloc(%d) text area\n", poolsz); return -1; }//// current position in emitted code
-  if (!(data = malloc(poolsz))) { printf("could not malloc(%d) data area\n", poolsz); return -1; }//数据段
-  if (!(sp = malloc(poolsz))) { printf("could not malloc(%d) stack area\n", poolsz); return -1; }//栈
-
-  memset(sym,  0, poolsz);
-  memset(e,    0, poolsz);
-  memset(data, 0, poolsz);
-
-  // 用词法分析器先把这些关键词放进符号表
-  p = "char else enum if int return sizeof while "
-      "open read close printf malloc memset memcmp exit void main";
-  // 把关键词加进去,id[Tk]修改为和Enum一致
-  i = Char; while (i <= While) { next(); id[Tk] = i++; } // add keywords to symbol table
-  //把[库]里定义的符号(系统函数等) 加进去 Class 赋值为Sys
-  i = OPEN; while (i <= EXIT) { next(); id[Class] = Sys; id[Type] = INT; id[Val] = i++; } // add library to symbol table
-  // void 认为是char
-  next(); id[Tk] = Char; // handle void type
-  // 记录main函数的符号id
-  next(); idmain = id; // keep track of main
-
-  if (!(lp = p = malloc(poolsz))) { printf("could not malloc(%d) source area\n", poolsz); return -1; }
-  if ((i = read(fd, p, poolsz-1)) <= 0) { printf("read() returned %d\n", i); return -1; }
-  p[i] = 0;//字符串结尾置0
-  close(fd);
-
-  // parse declarations
-  line = 1;
-  next();
-  while (tk) {
-    bt = INT; // basetype
-    if (tk == Int) next(); //已经有bt == INT
-    else if (tk == Char) { next(); bt = CHAR; }//char 变量;
-    else if (tk == Enum) {
-      next();
-      if (tk != '{') next(); // 似乎忽略了枚举名,例如 enum xxx{}
-      if (tk == '{') {
-        next();
-        i = 0; //Enum 默认从0 开始
-        while (tk != '}') {
-          if (tk != Id) { printf("%d: bad enum identifier %d\n", line, tk); return -1; } //不是Identifier 就出错
-          next();
-          if (tk == Assign) { // 发现赋值语句 如 enum { Num = 128 };
-            next();
-            if (tk != Num) { printf("%d: bad enum initializer\n", line); return -1; }
-            i = ival;
-            next();
-          }
-          //id 已经由 next 函数处理过
-          id[Class] = Num; id[Type] = INT; id[Val] = i++;
-          if (tk == ',') next();
-        }
-        next();
-      }
-    }
-    //Enum 处理完tk == ';', 略过下面
-    while (tk != ';' && tk != '}') {
-      ty = bt;//type 类型
-      while (tk == Mul) { next(); ty = ty + PTR; } // tk == Mul 表示已*开头,为指针类型,类型加PTR表示何种类型的指针
-      if (tk != Id) { printf("%d: bad global declaration\n", line); return -1; }
-      if (id[Class]) { printf("%d: duplicate global definition\n", line); return -1; } //重复全局变量定义,解释见后
-      next();
-      id[Type] = ty; //赋值类型
-      if (tk == '(') { // 函数
-        id[Class] = Fun;//类型为函数型
-        id[Val] = (int)(e + 1); //函数指针? 在字节码中的偏移量/地址
-        next(); i = 0;
-        while (tk != ')') {//参数列表
-          ty = INT;
-          if (tk == Int) next();
-          else if (tk == Char) { next(); ty = CHAR; }
-          while (tk == Mul) { next(); ty = ty + PTR; }
-          if (tk != Id) { printf("%d: bad parameter declaration\n", line); return -1; }
-          if (id[Class] == Loc) { printf("%d: duplicate parameter definition\n", line); return -1; } //函数参数是局部变量
-          //备份符号信息,要进入函数上下文了
-          id[HClass] = id[Class]; id[Class] = Loc;
-          id[HType]  = id[Type];  id[Type] = ty;
-          id[HVal]   = id[Val];   id[Val] = i++;//局部变量编号
-          next();
-          if (tk == ',') next();
-        }
-        next();
-        if (tk != '{') { printf("%d: bad function definition\n", line); return -1; }
-        loc = ++i; //局部变量偏移量
-        next();
-        while (tk == Int || tk == Char) { //函数内变量声明
-          bt = (tk == Int) ? INT : CHAR;
-          next();
-          while (tk != ';') {
-            ty = bt;
-            while (tk == Mul) { next(); ty = ty + PTR; }//处理指针型
-            if (tk != Id) { printf("%d: bad local declaration\n", line); return -1; }
-            if (id[Class] == Loc) { printf("%d: duplicate local definition\n", line); return -1; }
-            //备份符号信息
-            id[HClass] = id[Class]; id[Class] = Loc;
-            id[HType]  = id[Type];  id[Type] = ty;
-            id[HVal]   = id[Val];   id[Val] = ++i; //存储变量偏移量
-            next();
-            if (tk == ',') next();
-          }
-          next();
-        }
-        *++e = ENT; *++e = i - loc;//函数局部变量数目
-        while (tk != '}') stmt();//语法分析?
-        *++e = LEV;//函数返回
-        id = sym; // unwind symbol table locals
-        while (id[Tk]) {
-          //恢复符号信息
-          if (id[Class] == Loc) {
-            id[Class] = id[HClass];
-            id[Type] = id[HType];
-            id[Val] = id[HVal];
-          }
-          id = id + Idsz;
-        }
-      }
-      else {
-        id[Class] = Glo;//全局变量
-        id[Val] = (int)data;//给全局变量在data段分配内存
-        data = data + sizeof(int);
-      }
-      if (tk == ',') next();
-    }
-    next();
-  }
-
-  if (!(pc = (int *)idmain[Val])) { printf("main() not defined\n"); return -1; }
-  if (src) return 0;
-
-  // setup stack
-  sp = (int *)((int)sp + poolsz);
-  *--sp = EXIT; // call exit if main returns
-  *--sp = PSH; t = sp;
-  *--sp = argc;
-  *--sp = (int)argv;
-  *--sp = (int)t;
-
-  // run...
-  cycle = 0;
-  while (1) {
-    i = *pc++; ++cycle;
-    if (debug) {
-      printf("%d> %.4s", cycle,
-        &"LEA ,IMM ,JMP ,JSR ,BZ  ,BNZ ,ENT ,ADJ ,LEV ,LI  ,LC  ,SI  ,SC  ,PSH ,"
-         "OR  ,XOR ,AND ,EQ  ,NE  ,LT  ,GT  ,LE  ,GE  ,SHL ,SHR ,ADD ,SUB ,MUL ,DIV ,MOD ,"
-         "OPEN,READ,CLOS,PRTF,MALC,MSET,MCMP,EXIT,"[i * 5]);
-      if (i <= ADJ) printf(" %d\n", *pc); else printf("\n");
-    }
-    if      (i == LEA) a = (int)(bp + *pc++);                             // load local address
-    else if (i == IMM) a = *pc++;                                         // load global address or immediate
-    else if (i == JMP) pc = (int *)*pc;                                   // jump
-    else if (i == JSR) { *--sp = (int)(pc + 1); pc = (int *)*pc; }        // jump to subroutine
-    else if (i == BZ)  pc = a ? pc + 1 : (int *)*pc;                      // branch if zero
-    else if (i == BNZ) pc = a ? (int *)*pc : pc + 1;                      // branch if not zero
-    else if (i == ENT) { *--sp = (int)bp; bp = sp; sp = sp - *pc++; }     // enter subroutine
-    else if (i == ADJ) sp = sp + *pc++;                                   // stack adjust
-    else if (i == LEV) { sp = bp; bp = (int *)*sp++; pc = (int *)*sp++; } // leave subroutine
-    else if (i == LI)  a = *(int *)a;                                     // load int
-    else if (i == LC)  a = *(char *)a;                                    // load char
-    else if (i == SI)  *(int *)*sp++ = a;                                 // store int
-    else if (i == SC)  a = *(char *)*sp++ = a;                            // store char
-    else if (i == PSH) *--sp = a;                                         // push
-
-    else if (i == OR)  a = *sp++ |  a;
-    else if (i == XOR) a = *sp++ ^  a;
-    else if (i == AND) a = *sp++ &  a;
-    else if (i == EQ)  a = *sp++ == a;
-    else if (i == NE)  a = *sp++ != a;
-    else if (i == LT)  a = *sp++ <  a;
-    else if (i == GT)  a = *sp++ >  a;
-    else if (i == LE)  a = *sp++ <= a;
-    else if (i == GE)  a = *sp++ >= a;
-    else if (i == SHL) a = *sp++ << a;
-    else if (i == SHR) a = *sp++ >> a;
-    else if (i == ADD) a = *sp++ +  a;
-    else if (i == SUB) a = *sp++ -  a;
-    else if (i == MUL) a = *sp++ *  a;
-    else if (i == DIV) a = *sp++ /  a;
-    else if (i == MOD) a = *sp++ %  a;
-
-    else if (i == OPEN) a = open((char *)sp[1], *sp);
-    else if (i == READ) a = read(sp[2], (char *)sp[1], *sp);
-    else if (i == CLOS) a = close(*sp);
-    else if (i == PRTF) { t = sp + pc[1]; a = printf((char *)t[-1], t[-2], t[-3], t[-4], t[-5], t[-6]); }
-    else if (i == MALC) a = (int)malloc(*sp);
-    else if (i == MSET) a = (int)memset((char *)sp[2], sp[1], *sp);
-    else if (i == MCMP) a = memcmp((char *)sp[2], (char *)sp[1], *sp);
-    else if (i == EXIT) { printf("exit(%d) cycle = %d\n", *sp, cycle); return *sp; }
-    else { printf("unknown instruction = %d! cycle = %d\n", i, cycle); return -1; }
-  }
-}
+// c4.c - C in four functions
+
+// char, int, and pointer types
+// if, while, return, and expression statements
+// just enough features to allow self-compilation and a bit more
+
+// Written by Robert Swierczek
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <memory.h>
+#include <unistd.h>
+
+char *p, *lp, // current position in source code
+     *data;   // data/bss pointer
+
+int *e, *le,  // current position in emitted code
+    *id,      // currently parsed identifier
+    *sym,     // symbol table (simple list of identifiers)
+    tk,       // current token
+    ival,     // current token value
+    ty,       // current expression type
+    loc,      // local variable offset
+    line,     // current line number
+    src,      // print source and assembly flag
+    debug;    // print executed instructions
+
+// tokens and classes (operators last and in precedence order)
+/*
+
+Id = identifier 用户定义的identifier
+
+//运算符
+Assign  =
+Cond    ?
+Lor     ||
+Lan     &&
+Or      |
+Xor     ^
+And     &
+Eq      ==
+Ne      !=
+Lt      <
+Gt      >
+Le      <=
+Ge      >=
+Shl     <<
+Shr     >>
+Add     +
+Sub     -
+Mul     *
+Div     /
+Mod     %
+Inc     ++
+Dec     --
+Brak    [
+*/
+/*
+id[Class] =
+Num  常量数值
+Fun 函数
+Sys 系统调用
+Glo 全局变量
+Loc 局部变量
+*/
+enum {
+  Num = 128, Fun, Sys, Glo, Loc, Id,
+  Char, Else, Enum, If, Int, Return, Sizeof, While,
+  Assign, Cond, Lor, Lan, Or, Xor, And, Eq, Ne, Lt, Gt, Le, Ge, Shl, Shr, Add, Sub, Mul, Div, Mod, Inc, Dec, Brak
+};
+
+// opcodes
+enum { LEA ,IMM ,JMP ,JSR ,BZ  ,BNZ ,ENT ,ADJ ,LEV ,LI  ,LC  ,SI  ,SC  ,PSH ,
+       OR  ,XOR ,AND ,EQ  ,NE  ,LT  ,GT  ,LE  ,GE  ,SHL ,SHR ,ADD ,SUB ,MUL ,DIV ,MOD ,
+       OPEN,READ,CLOS,PRTF,MALC,MSET,MCMP,EXIT };
+
+// types
+enum { CHAR, INT, PTR };
+
+// identifier offsets (since we can't create an ident struct)
+//因为作者没有实现结构体,所以[id]指向的空间被分割为Idsz大小的块(模拟结构体)
+//当id指向块首时,id[0] == id[Tk] 访问的就是Tk成员的数据(一般是指针)
+//Name 指向的是这个identifier的Name
+//Type 为数据类型(比如返回值类型),如CHAR,INT,INT+PTR
+//Class 为类型,如Num(常量数值),Fun(函数),Sys(系统调用),Glo全局变量,Loc 局部变量
+enum { Tk, Hash, Name, Class, Type, Val, HClass, HType, HVal, Idsz };
+
+//词法分析
+void next()
+{
+  char *pp;
+  // 用循环来忽略空白字符,不过不能被词法分析器识别的字符都被认为是空白字符 比如 '@', '$'
+  while (tk = *p) {
+    ++p;
+    if (tk == '\n') {
+      if (src) { //命令行指明-s参数,输出源代码和对应字节码
+        printf("%d: %.*s", line, p - lp, lp);
+        lp = p;
+        while (le < e) {
+          printf("%8.4s", &"LEA ,IMM ,JMP ,JSR ,BZ  ,BNZ ,ENT ,ADJ ,LEV ,LI  ,LC  ,SI  ,SC  ,PSH ,"
+                           "OR  ,XOR ,AND ,EQ  ,NE  ,LT  ,GT  ,LE  ,GE  ,SHL ,SHR ,ADD ,SUB ,MUL ,DIV ,MOD ,"
+                           "OPEN,READ,CLOS,PRTF,MALC,MSET,MCMP,EXIT,"[*++le * 5]);
+          if (*le <= ADJ) printf(" %d\n", *++le); else printf("\n"); //ADJ之前的指令均有操作数
+        }
+      }
+      ++line;
+    }
+    else if (tk == '#') {//#作为单行注释符号,处理#include等情况
+      while (*p != 0 && *p != '\n') ++p;
+    }
+    else if ((tk >= 'a' && tk <= 'z') || (tk >= 'A' && tk <= 'Z') || tk == '_') {
+      pp = p - 1; //因为有++p,pp回退一个字符,pp指向 [这个符号] 的首字母
+      while ((*p >= 'a' && *p <= 'z') || (*p >= 'A' && *p <= 'Z') || (*p >= '0' && *p <= '9') || *p == '_')
+        tk = tk * 147 + *p++;//计算哈希值,tk起始时已经等于*p,从p开始正确
+      tk = (tk << 6) + (p - pp); //哈希值加上[符号长度]
+      id = sym;
+      while (id[Tk]) {
+        if (tk == id[Hash] && !memcmp((char *)id[Name], pp, p - pp)) {
+          //找到同名,则tk = id[Tk] (将id看做结构体,访问其Tk成员,解释见上)
+          tk = id[Tk];
+          return;
+        }
+        id = id + Idsz;//继续循环identifier表
+      }
+      //找不到,发现新identifier,此时id已经指向新的identifier结构
+      id[Name] = (int)pp;
+      id[Hash] = tk;//哈希值
+      tk = id[Tk] = Id; //token 类型为identifier
+      return;
+    }
+    else if (tk >= '0' && tk <= '9') {// 第一位为数字,认为是数值
+      if (ival = tk - '0') { while (*p >= '0' && *p <= '9') ival = ival * 10 + *p++ - '0'; }//第一位不为0,认为是十进制数
+      else if (*p == 'x' || *p == 'X') {//第一位为0,且以x开头,认为是16进制数
+        while ((tk = *++p) && ((tk >= '0' && tk <= '9') || (tk >= 'a' && tk <= 'f') || (tk >= 'A' && tk <= 'F')))
+          ival = ival * 16 + (tk & 15) + (tk >= 'A' ? 9 : 0);
+      }
+      else { while (*p >= '0' && *p <= '7') ival = ival * 8 + *p++ - '0'; }//认为是八进制数
+      tk = Num;//token 为数值型,返回
+      return;
+    }
+    else if (tk == '/') {
+      if (*p == '/') {//两个'/'开头,单行注释
+        ++p;
+        while (*p != 0 && *p != '\n') ++p;
+      }
+      else {
+        tk = Div; //除法
+        return;
+      }
+    }
+    else if (tk == '\'' || tk == '"') {//引号开头,认为是字符(串)
+      pp = data;
+      while (*p != 0 && *p != tk) {//直到找到匹配的引号或文件末尾为止
+        if ((ival = *p++) == '\\') {
+          if ((ival = *p++) == 'n') ival = '\n';// '\n' 认为是'\n' 其他直接忽略'\'转义
+        }
+        if (tk == '"') *data++ = ival;//如果是双引号,认为是字符串,向data拷贝字符
+      }
+      ++p;
+      if (tk == '"') ival = (int)pp; else tk = Num;//双引号则ival指向data中字符串开始,单引号则认为是数字
+      return;
+    }
+    else if (tk == '=') { if (*p == '=') { ++p; tk = Eq; } else tk = Assign; return; }//等于,赋值
+    else if (tk == '+') { if (*p == '+') { ++p; tk = Inc; } else tk = Add; return; }//加,自增
+    else if (tk == '-') { if (*p == '-') { ++p; tk = Dec; } else tk = Sub; return; }//减,自减
+    else if (tk == '!') { if (*p == '=') { ++p; tk = Ne; } return; }//不等于
+    else if (tk == '<') { if (*p == '=') { ++p; tk = Le; } else if (*p == '<') { ++p; tk = Shl; } else tk = Lt; return; }// <,<=, <<
+    else if (tk == '>') { if (*p == '=') { ++p; tk = Ge; } else if (*p == '>') { ++p; tk = Shr; } else tk = Gt; return; }//>,>= >>
+    else if (tk == '|') { if (*p == '|') { ++p; tk = Lor; } else tk = Or; return; }//逻辑或,或
+    else if (tk == '&') { if (*p == '&') { ++p; tk = Lan; } else tk = And; return; }
+    else if (tk == '^') { tk = Xor; return; }
+    else if (tk == '%') { tk = Mod; return; }
+    else if (tk == '*') { tk = Mul; return; }
+    else if (tk == '[') { tk = Brak; return; }
+    else if (tk == '?') { tk = Cond; return; }
+    else if (tk == '~' || tk == ';' || tk == '{' || tk == '}' || tk == '(' || tk == ')' || tk == ']' || tk == ',' || tk == ':') return;//不做处理
+  }
+}
+//表达式分析
+//lev表示运算符,因为各个运算符token是按照优先级生序排列的,所以lev大表示优先级高
+void expr(int lev)
+{
+  int t, *d;
+
+  if (!tk) { printf("%d: unexpected eof in expression\n", line); exit(-1); }
+  else if (tk == Num) { *++e = IMM; *++e = ival; next(); ty = INT; } //直接取立即数作为表达式值
+  else if (tk == '"') { //字符串
+    *++e = IMM; *++e = ival; next();
+    while (tk == '"') next();//连续的'"' 处理C风格多行文本 比如["abc" "def"]
+    data = (char *)((int)data + sizeof(int) & -sizeof(int));//字节对齐到int
+    ty = PTR;
+  }
+  else if (tk == Sizeof) {
+    next(); if (tk == '(') next(); else { printf("%d: open paren expected in sizeof\n", line); exit(-1); }
+    ty = INT; if (tk == Int) next(); else if (tk == Char) { next(); ty = CHAR; }
+    while (tk == Mul) { next(); ty = ty + PTR; }//多级指针,每多一级加PTR
+    if (tk == ')') next(); else { printf("%d: close paren expected in sizeof\n", line); exit(-1); }
+    *++e = IMM; *++e = (ty == CHAR) ? sizeof(char) : sizeof(int);//除了char是一字节,int和多级指针都是int大小
+    ty = INT;
+  }
+  else if (tk == Id) {//identifier
+    d = id; next();
+    if (tk == '(') {//函数
+      next();
+      t = 0;//形参个数
+      while (tk != ')') { expr(Assign); *++e = PSH; ++t; if (tk == ',') next(); }//计算实参的值，压栈(传参)
+      next();
+      if (d[Class] == Sys) *++e = d[Val]; //系统调用,如malloc,memset,d[val]为opcode
+      else if (d[Class] == Fun) { *++e = JSR; *++e = d[Val]; } //用户定义函数,d[Val]为函数入口地址
+      else { printf("%d: bad function call\n", line); exit(-1); }
+      if (t) { *++e = ADJ; *++e = t; }//因为用栈传参,调整栈
+      ty = d[Type];//函数返回值类型
+    }
+    else if (d[Class] == Num) { *++e = IMM; *++e = d[Val]; ty = INT; }//d[Class] == Num,处理枚举(只有枚举是Class==Num)
+    else {//变量
+      //变量先取地址然后再LC/LI
+      if (d[Class] == Loc) { *++e = LEA; *++e = loc - d[Val]; }//取地址,d[Val]是局部变量偏移量
+      else if (d[Class] == Glo) { *++e = IMM; *++e = d[Val]; }//取地址,d[Val] 是全局变量指针
+      else { printf("%d: undefined variable\n", line); exit(-1); }
+      *++e = ((ty = d[Type]) == CHAR) ? LC : LI;
+    }
+  }
+  else if (tk == '(') {
+    next();
+    if (tk == Int || tk == Char) {//强制类型转换
+      t = (tk == Int) ? INT : CHAR; next();
+      while (tk == Mul) { next(); t = t + PTR; }//指针
+      if (tk == ')') next(); else { printf("%d: bad cast\n", line); exit(-1); }
+      expr(Inc); //高优先级
+      ty = t;
+    }
+    else { //一般语法括号
+      expr(Assign);
+      if (tk == ')') next(); else { printf("%d: close paren expected\n", line); exit(-1); }
+    }
+  }
+  else if (tk == Mul) {//取指针指向值
+    next(); expr(Inc);//高优先级
+    if (ty > INT) ty = ty - PTR; else { printf("%d: bad dereference\n", line); exit(-1); }
+    *++e = (ty == CHAR) ? LC : LI;
+  }
+  else if (tk == And) {//&,取地址操作
+    next(); expr(Inc);
+    if (*e == LC || *e == LI) --e;//根据上面的代码,token为变量时都是先取地址再LI/LC,所以--e就变成了取地址到a
+    else { printf("%d: bad address-of\n", line); exit(-1); }
+    ty = ty + PTR;
+  }
+  else if (tk == '!') { next(); expr(Inc); *++e = PSH; *++e = IMM; *++e = 0; *++e = EQ; ty = INT; }//!x相当于 x==0
+  else if (tk == '~') { next(); expr(Inc); *++e = PSH; *++e = IMM; *++e = -1; *++e = XOR; ty = INT; }//~x 相当于x ^ -1
+  else if (tk == Add) { next(); expr(Inc); ty = INT; }
+  else if (tk == Sub) {
+    next(); *++e = IMM;
+    if (tk == Num) { *++e = -ival; next(); } //数值,取负
+    else { *++e = -1; *++e = PSH; expr(Inc); *++e = MUL; }//乘-1
+    ty = INT;
+  }
+  else if (tk == Inc || tk == Dec) {//处理++x,--x//x--,x++在后面处理
+    t = tk; next(); expr(Inc);
+    //处理++x,--x
+    if (*e == LC) { *e = PSH; *++e = LC; }//地址压栈(下面SC/SI用到),再取数
+    else if (*e == LI) { *e = PSH; *++e = LI; }
+    else { printf("%d: bad lvalue in pre-increment\n", line); exit(-1); }
+    *++e = PSH;//将数值压栈
+    *++e = IMM; *++e = (ty > PTR) ? sizeof(int) : sizeof(char);//指针则加减一字,否则加减1
+    *++e = (t == Inc) ? ADD : SUB;//运算
+    *++e = (ty == CHAR) ? SC : SI;//存回变量
+  }
+  else { printf("%d: bad expression\n", line); exit(-1); }
+
+  //爬山法
+  //tk为ASCII码的都不会超过Num=128
+  while (tk >= lev) { // "precedence climbing" or "Top Down Operator Precedence" method
+    t = ty;//ty在递归过程中可能会改变,所以备份当前处理的表达式类型
+    if (tk == Assign) { //赋值
+      next();
+      if (*e == LC || *e == LI) *e = PSH; //左边被tk=Id中变量部分处理过了,将地址压栈
+      else { printf("%d: bad lvalue in assignment\n", line); exit(-1); }
+      expr(Assign); *++e = ((ty = t) == CHAR) ? SC : SI;//取得右值expr的值,作为a=expr的结果
+    }
+    else if (tk == Cond) {//x?a:b和if类似,除了不能没有else
+      next();
+      *++e = BZ; d = ++e;
+      expr(Assign);
+      if (tk == ':') next(); else { printf("%d: conditional missing colon\n", line); exit(-1); }
+      *d = (int)(e + 3); *++e = JMP; d = ++e;
+      expr(Cond);
+      *d = (int)(e + 1);
+    }
+    else if (tk == Lor) { next(); *++e = BNZ; d = ++e; expr(Lan); *d = (int)(e + 1); ty = INT; }//短路,逻辑Or运算符左边为true则表达式为true,不用计算运算符右侧的值
+    else if (tk == Lan) { next(); *++e = BZ;  d = ++e; expr(Or);  *d = (int)(e + 1); ty = INT; }//短路,逻辑And,同上
+    else if (tk == Or)  { next(); *++e = PSH; expr(Xor); *++e = OR;  ty = INT; }//将当前值Push,计算运算符右边值,再与当前值(在栈中)做运算;
+    else if (tk == Xor) { next(); *++e = PSH; expr(And); *++e = XOR; ty = INT; }//expr中lev指明递归函数中最结合性不得低于哪一个运算符
+    else if (tk == And) { next(); *++e = PSH; expr(Eq);  *++e = AND; ty = INT; }
+    else if (tk == Eq)  { next(); *++e = PSH; expr(Lt);  *++e = EQ;  ty = INT; }
+    else if (tk == Ne)  { next(); *++e = PSH; expr(Lt);  *++e = NE;  ty = INT; }
+    else if (tk == Lt)  { next(); *++e = PSH; expr(Shl); *++e = LT;  ty = INT; }
+    else if (tk == Gt)  { next(); *++e = PSH; expr(Shl); *++e = GT;  ty = INT; }
+    else if (tk == Le)  { next(); *++e = PSH; expr(Shl); *++e = LE;  ty = INT; }
+    else if (tk == Ge)  { next(); *++e = PSH; expr(Shl); *++e = GE;  ty = INT; }
+    else if (tk == Shl) { next(); *++e = PSH; expr(Add); *++e = SHL; ty = INT; }
+    else if (tk == Shr) { next(); *++e = PSH; expr(Add); *++e = SHR; ty = INT; }
+    else if (tk == Add) {
+      next(); *++e = PSH; expr(Mul);
+      if ((ty = t) > PTR) { *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = MUL;  }//处理指针
+      *++e = ADD;
+    }
+    else if (tk == Sub) {
+      next(); *++e = PSH; expr(Mul);
+      if (t > PTR && t == ty) { *++e = SUB; *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = DIV; ty = INT; }//指针相减
+      else if ((ty = t) > PTR) { *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = MUL; *++e = SUB; }//指针减数值
+      else *++e = SUB;
+    }
+    else if (tk == Mul) { next(); *++e = PSH; expr(Inc); *++e = MUL; ty = INT; }
+    else if (tk == Div) { next(); *++e = PSH; expr(Inc); *++e = DIV; ty = INT; }
+    else if (tk == Mod) { next(); *++e = PSH; expr(Inc); *++e = MOD; ty = INT; }
+    else if (tk == Inc || tk == Dec) {//处理x++,x--
+      if (*e == LC) { *e = PSH; *++e = LC; }
+      else if (*e == LI) { *e = PSH; *++e = LI; }
+      else { printf("%d: bad lvalue in post-increment\n", line); exit(-1); }
+      *++e = PSH; *++e = IMM; *++e = (ty > PTR) ? sizeof(int) : sizeof(char);
+      *++e = (tk == Inc) ? ADD : SUB;//先自增/自减
+      *++e = (ty == CHAR) ? SC : SI;//存到内存里
+      *++e = PSH; *++e = IMM; *++e = (ty > PTR) ? sizeof(int) : sizeof(char);
+      *++e = (tk == Inc) ? SUB : ADD;//再相反操作,保证后自增/自减不影响这次表达式的求值
+      //PS:我终于知道哪些a=1;b=a+++a++为啥等于3了
+      next();
+    }
+    else if (tk == Brak) {//数组下标
+      next(); *++e = PSH; expr(Assign);//保存数组指针, 计算下标
+      if (tk == ']') next(); else { printf("%d: close bracket expected\n", line); exit(-1); }
+      if (t > PTR) { *++e = PSH; *++e = IMM; *++e = sizeof(int); *++e = MUL;  } //t==PTR时是Char,Char = 0
+      else if (t < PTR) { printf("%d: pointer type expected\n", line); exit(-1); }
+      *++e = ADD;
+      *++e = ((ty = t - PTR) == CHAR) ? LC : LI;
+    }
+    else { printf("%d: compiler error tk=%d\n", line, tk); exit(-1); }
+  }
+}
+
+//分析函数中除了声明之外的部分,语法分析
+void stmt()
+{
+  int *a, *b;
+
+  if (tk == If) {
+    next();
+    if (tk == '(') next(); else { printf("%d: open paren expected\n", line); exit(-1); }
+    expr(Assign);
+    if (tk == ')') next(); else { printf("%d: close paren expected\n", line); exit(-1); }
+    *++e = BZ; //branch if zero
+    b = ++e;//branch address pointer
+    stmt(); // 继续分析
+    if (tk == Else) {
+      *b = (int)(e + 3); // e + 3 位置是else 起始位置
+      *++e = JMP; // if 语句 else 之前插入 JMP 跳过Else 部分
+      b = ++e; // JMP目标
+      next();
+      stmt();//分析else 部分
+    }
+    *b = (int)(e + 1);//if 语句结束,无论是if BZ 跳转目标还是 else 之前的JMP的跳转目标
+  }
+  else if (tk == While) {//循环
+    next();
+    a = e + 1; // While 循环体起始地址
+    if (tk == '(') next(); else { printf("%d: open paren expected\n", line); exit(-1); }
+    expr(Assign);
+    if (tk == ')') next(); else { printf("%d: close paren expected\n", line); exit(-1); }
+    *++e = BZ; b = ++e;//b = While 语句结束后地址
+    stmt();//处理While 语句体
+    *++e = JMP; *++e = (int)a;//无条件跳转到While语句开始(包括循环条件的代码),实现循环
+    *b = (int)(e + 1);//BZ跳转目标(循环结束)
+  }
+  else if (tk == Return) {
+    next();
+    if (tk != ';') expr(Assign);//计算返回值
+    *++e = LEV;
+    if (tk == ';') next(); else { printf("%d: semicolon expected\n", line); exit(-1); }//What's this?
+  }
+  else if (tk == '{') {//复合语句
+    next();
+    while (tk != '}') stmt();
+    next();
+  }
+  else if (tk == ';') {
+    next();
+  }
+  else {
+    expr(Assign);//一般的语句认为是赋值语句/表达式
+    if (tk == ';') next(); else { printf("%d: semicolon expected\n", line); exit(-1); }
+  }
+}
+
+int main(int argc, char **argv)
+{
+  //fd file descriptor 文件描述
+  //bt basetype
+  //poolsz 一系列池的大小
+  int fd, bt, ty, poolsz, *idmain;
+  int *pc, *sp, *bp, a, cycle; // vm registers 虚拟器的寄存器
+  int i, *t; // temps
+
+  --argc; ++argv;
+  if (argc > 0 && **argv == '-' && (*argv)[1] == 's') { src = 1; --argc; ++argv; }
+  if (argc > 0 && **argv == '-' && (*argv)[1] == 'd') { debug = 1; --argc; ++argv; }
+  if (argc < 1) { printf("usage: c4 [-s] [-d] file ...\n"); return -1; }
+
+  if ((fd = open(*argv, 0)) < 0) { printf("could not open(%s)\n", *argv); return -1; }//打开文件
+
+  poolsz = 256*1024; // arbitrary size
+  if (!(sym = malloc(poolsz))) { printf("could not malloc(%d) symbol area\n", poolsz); return -1; }//符号表
+  if (!(le = e = malloc(poolsz))) { printf("could not malloc(%d) text area\n", poolsz); return -1; }//// current position in emitted code
+  if (!(data = malloc(poolsz))) { printf("could not malloc(%d) data area\n", poolsz); return -1; }//数据段
+  if (!(sp = malloc(poolsz))) { printf("could not malloc(%d) stack area\n", poolsz); return -1; }//栈
+
+  memset(sym,  0, poolsz);
+  memset(e,    0, poolsz);
+  memset(data, 0, poolsz);
+
+  // 用词法分析器先把这些关键词放进符号表
+  p = "char else enum if int return sizeof while "
+      "open read close printf malloc memset memcmp exit void main";
+  // 把关键词加进去,id[Tk]修改为和Enum一致
+  i = Char; while (i <= While) { next(); id[Tk] = i++; } // add keywords to symbol table
+  //把[库]里定义的符号(系统函数等) 加进去 Class 赋值为Sys
+  i = OPEN; while (i <= EXIT) { next(); id[Class] = Sys; id[Type] = INT; id[Val] = i++; } // add library to symbol table
+  // void 认为是char
+  next(); id[Tk] = Char; // handle void type
+  // 记录main函数的符号id
+  next(); idmain = id; // keep track of main
+
+  if (!(lp = p = malloc(poolsz))) { printf("could not malloc(%d) source area\n", poolsz); return -1; }
+  if ((i = read(fd, p, poolsz-1)) <= 0) { printf("read() returned %d\n", i); return -1; }
+  p[i] = 0;//字符串结尾置0
+  close(fd);
+
+  // parse declarations
+  line = 1;
+  next();
+  while (tk) {
+    bt = INT; // basetype
+    if (tk == Int) next(); //已经有bt == INT
+    else if (tk == Char) { next(); bt = CHAR; }//char 变量;
+    else if (tk == Enum) {
+      next();
+      if (tk != '{') next(); // 似乎忽略了枚举名,例如 enum xxx{}
+      if (tk == '{') {
+        next();
+        i = 0; //Enum 默认从0 开始
+        while (tk != '}') {
+          if (tk != Id) { printf("%d: bad enum identifier %d\n", line, tk); return -1; } //不是Identifier 就出错
+          next();
+          if (tk == Assign) { // 发现赋值语句 如 enum { Num = 128 };
+            next();
+            if (tk != Num) { printf("%d: bad enum initializer\n", line); return -1; }
+            i = ival;
+            next();
+          }
+          //id 已经由 next 函数处理过
+          id[Class] = Num; id[Type] = INT; id[Val] = i++;
+          if (tk == ',') next();
+        }
+        next();
+      }
+    }
+    //Enum 处理完tk == ';', 略过下面
+    while (tk != ';' && tk != '}') {
+      ty = bt;//type 类型
+      while (tk == Mul) { next(); ty = ty + PTR; } // tk == Mul 表示已*开头,为指针类型,类型加PTR表示何种类型的指针
+      if (tk != Id) { printf("%d: bad global declaration\n", line); return -1; }
+      if (id[Class]) { printf("%d: duplicate global definition\n", line); return -1; } //重复全局变量定义,解释见后
+      next();
+      id[Type] = ty; //赋值类型
+      if (tk == '(') { // 函数
+        id[Class] = Fun;//类型为函数型
+        id[Val] = (int)(e + 1); //函数指针? 在字节码中的偏移量/地址
+        next(); i = 0;
+        while (tk != ')') {//参数列表
+          ty = INT;
+          if (tk == Int) next();
+          else if (tk == Char) { next(); ty = CHAR; }
+          while (tk == Mul) { next(); ty = ty + PTR; }
+          if (tk != Id) { printf("%d: bad parameter declaration\n", line); return -1; }
+          if (id[Class] == Loc) { printf("%d: duplicate parameter definition\n", line); return -1; } //函数参数是局部变量
+          //备份符号信息,要进入函数上下文了
+          id[HClass] = id[Class]; id[Class] = Loc;
+          id[HType]  = id[Type];  id[Type] = ty;
+          id[HVal]   = id[Val];   id[Val] = i++;//局部变量编号
+          next();
+          if (tk == ',') next();
+        }
+        next();
+        if (tk != '{') { printf("%d: bad function definition\n", line); return -1; }
+        loc = ++i; //局部变量偏移量
+        next();
+        while (tk == Int || tk == Char) { //函数内变量声明
+          bt = (tk == Int) ? INT : CHAR;
+          next();
+          while (tk != ';') {
+            ty = bt;
+            while (tk == Mul) { next(); ty = ty + PTR; }//处理指针型
+            if (tk != Id) { printf("%d: bad local declaration\n", line); return -1; }
+            if (id[Class] == Loc) { printf("%d: duplicate local definition\n", line); return -1; }
+            //备份符号信息
+            id[HClass] = id[Class]; id[Class] = Loc;
+            id[HType]  = id[Type];  id[Type] = ty;
+            id[HVal]   = id[Val];   id[Val] = ++i; //存储变量偏移量
+            next();
+            if (tk == ',') next();
+          }
+          next();
+        }
+        *++e = ENT; *++e = i - loc;//函数局部变量数目
+        while (tk != '}') stmt();//语法分析?
+        *++e = LEV;//函数返回
+        id = sym; // unwind symbol table locals
+        while (id[Tk]) {
+          //恢复符号信息
+          if (id[Class] == Loc) {
+            id[Class] = id[HClass];
+            id[Type] = id[HType];
+            id[Val] = id[HVal];
+          }
+          id = id + Idsz;
+        }
+      }
+      else {
+        id[Class] = Glo;//全局变量
+        id[Val] = (int)data;//给全局变量在data段分配内存
+        data = data + sizeof(int);
+      }
+      if (tk == ',') next();
+    }
+    next();
+  }
+
+  if (!(pc = (int *)idmain[Val])) { printf("main() not defined\n"); return -1; }
+  if (src) return 0;
+
+  // setup stack
+  sp = (int *)((int)sp + poolsz);
+  *--sp = EXIT; // call exit if main returns
+  *--sp = PSH; t = sp;
+  *--sp = argc;
+  *--sp = (int)argv;
+  *--sp = (int)t;
+
+  // run...
+  cycle = 0;
+  while (1) {
+    i = *pc++; ++cycle;
+    if (debug) {
+      printf("%d> %.4s", cycle,
+        &"LEA ,IMM ,JMP ,JSR ,BZ  ,BNZ ,ENT ,ADJ ,LEV ,LI  ,LC  ,SI  ,SC  ,PSH ,"
+         "OR  ,XOR ,AND ,EQ  ,NE  ,LT  ,GT  ,LE  ,GE  ,SHL ,SHR ,ADD ,SUB ,MUL ,DIV ,MOD ,"
+         "OPEN,READ,CLOS,PRTF,MALC,MSET,MCMP,EXIT,"[i * 5]);
+      if (i <= ADJ) printf(" %d\n", *pc); else printf("\n");
+    }
+    if      (i == LEA) a = (int)(bp + *pc++);                             // load local address
+    else if (i == IMM) a = *pc++;                                         // load global address or immediate
+    else if (i == JMP) pc = (int *)*pc;                                   // jump
+    else if (i == JSR) { *--sp = (int)(pc + 1); pc = (int *)*pc; }        // jump to subroutine
+    else if (i == BZ)  pc = a ? pc + 1 : (int *)*pc;                      // branch if zero
+    else if (i == BNZ) pc = a ? (int *)*pc : pc + 1;                      // branch if not zero
+    else if (i == ENT) { *--sp = (int)bp; bp = sp; sp = sp - *pc++; }     // enter subroutine
+    else if (i == ADJ) sp = sp + *pc++;                                   // stack adjust
+    else if (i == LEV) { sp = bp; bp = (int *)*sp++; pc = (int *)*sp++; } // leave subroutine
+    else if (i == LI)  a = *(int *)a;                                     // load int
+    else if (i == LC)  a = *(char *)a;                                    // load char
+    else if (i == SI)  *(int *)*sp++ = a;                                 // store int
+    else if (i == SC)  a = *(char *)*sp++ = a;                            // store char
+    else if (i == PSH) *--sp = a;                                         // push
+
+    else if (i == OR)  a = *sp++ |  a;
+    else if (i == XOR) a = *sp++ ^  a;
+    else if (i == AND) a = *sp++ &  a;
+    else if (i == EQ)  a = *sp++ == a;
+    else if (i == NE)  a = *sp++ != a;
+    else if (i == LT)  a = *sp++ <  a;
+    else if (i == GT)  a = *sp++ >  a;
+    else if (i == LE)  a = *sp++ <= a;
+    else if (i == GE)  a = *sp++ >= a;
+    else if (i == SHL) a = *sp++ << a;
+    else if (i == SHR) a = *sp++ >> a;
+    else if (i == ADD) a = *sp++ +  a;
+    else if (i == SUB) a = *sp++ -  a;
+    else if (i == MUL) a = *sp++ *  a;
+    else if (i == DIV) a = *sp++ /  a;
+    else if (i == MOD) a = *sp++ %  a;
+
+    else if (i == OPEN) a = open((char *)sp[1], *sp);
+    else if (i == READ) a = read(sp[2], (char *)sp[1], *sp);
+    else if (i == CLOS) a = close(*sp);
+    else if (i == PRTF) { t = sp + pc[1]; a = printf((char *)t[-1], t[-2], t[-3], t[-4], t[-5], t[-6]); }
+    else if (i == MALC) a = (int)malloc(*sp);
+    else if (i == MSET) a = (int)memset((char *)sp[2], sp[1], *sp);
+    else if (i == MCMP) a = memcmp((char *)sp[2], (char *)sp[1], *sp);
+    else if (i == EXIT) { printf("exit(%d) cycle = %d\n", *sp, cycle); return *sp; }
+    else { printf("unknown instruction = %d! cycle = %d\n", i, cycle); return -1; }
+  }
+}